Last few days when I looked in to access.log and report using
lightsquid. I found usage report of some users are error. Report of
user1 showing websites those he never accessed to and it came from
user2. I don't know what could be the cause but I have tried restart
both Squid server and AD but report still the same.

I'm now using Squid 2.6 on CentOS box with 'winbind' for authentication.